Various techniques have been employed in the past for the polymerization of polymers and copolymers of olefins. One approach has involved employing catalysts containing chromium. Typically such polymerizations are carried out at relatively low temperatures and pressures.
For many applications, such as extrusion and molding processes, it is highly desirable to have polymers which have a broad molecular weight distribution. Such polymers exhibit excellent processability, i.e., they can be processed at a faster throughput rate with lower energy requirements with reduced melt flow perturbations.
Some techniques for preparing such polymers have involved the use of multiple reactor arrangements. Such multiple reactor schemes, while offering versatility in resin characteristics, can be less efficient than would be desired. Preparing the polymer in a single reactor would be much more economical.
It is also desirable to obtain a bimodal, or broad molecular weight distribution ethylene polymer in which comonomer is incorporated into the high molecular weight portion of the molecular weight distribution. Such polymers exhibit good impact resistance, tensile strength, elongation, flexural modulus, and environmental stress crack resistance.
In commercial applications, high bulk density is important for practical considerations such as convenient transfer and handling of the polymer. It is also important in commercial applications to be able to produce a wide spectrum of polymers so far as melt flow is concerned, i.e. molecular weight.
It would therefore be desirable to provide a catalyst capable of preparing polymers having high bulk density, broad molecular weight distribution with comonomer incorporated in the high molecular weight portion, while employing a single reactor.